Coulometric Study of Rates of Oxalic Acid Adsorption at a Polycrystalline Platinum Electrode

Report No. ARL-TR-6165
Authors: Sol Gilman
Date/Pages: September 2012; 26 pages
Abstract: Quantitative measurement of adsorption/desorption of oxalic acid on a platinum (Pt) electrode from a perchloric acid supporting electrolyte has been accomplished for the first time using a fast potential scan preceded by a sequence of potential steps. From a dilute solution of oxalic acid, adsorption of the anion is so rapid as to be diffusion-controlled over the range of potentials at which the surface is free of adsorbed oxygen; most of the final coverage achieved in less than a half-second. Cathodic desorption of the adsorbed anion occurs in the millisecond range. An isotherm for reversible adsorption applies to the range 0 to 0.9 V versus a reversible hydrogen electrode (RHE), but below 0.3 V, there is conversion to irreversible adsorption that is perceptible after hundreds of seconds. Irreversible adsorption blocks cathodic hydrogen adsorption while reversible adsorption does not. Adsorbed oxalic acid has a negative effect on the anodic oxidation of ethylene glycol and the reduction of molecular oxygen.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2012